Weight-compensating device

ABSTRACT

The present invention relates to a weight compensating device comprising a carrier and a component which is supported on the carrier and is displaceable particularly in vertical direction by means of a drive, characterized in that the carrier and the component have arranged thereinbetween at least one negative pressure body of a variable length which is connected to a negative pressure source for compensating the weight acting on the component.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a weight compensating device comprisinga carrier and a component which is supported on the carrier and isdisplaceable particularly in a vertical direction by means of a drive.

2. Background Information

Especially in the field of machine tools, components which are in partrelatively heavy must be displaced and/or precisely held in verticaldirection against their weight or against gravity.

Many mechanisms are already known wherein a weight compensating deviceis used for compensating at least part of the weight/gravity of thecomponent and for relieving the drive at the same time. The solutionsinclude, for instance, counterweights, which are e.g. held via adeflection pulley and a rope, or the like. Further mechanisms showhydraulic or pneumatic solutions.

The already known solutions are marked by the drawback that the sum ofthe masses to be moved will be increased considerably when acounterweight is used because the mass of the weight compensating devicehas to be added to the mass of the component.

The total mass which is increased on the whole entails serious problemswith respect to the inertia of the component. For instance, it is notpossible to move accelerations of more than 1 g because this willotherwise damage the weight compensating device or impair its functionalreliability. In particular, cables or the like, used by the weightcompensating device, cannot be held under tension for a long period oftime.

Further problems are created by accelerations that arise and necessarydecelerations.

In hydraulic and pneumatic solutions, additional friction is caused bythe use of hydraulic cylinders or pneumatic cylinders during movement ofthe component. This additional friction must be compensated by thedrive. Additional friction arises on account of the piston seals of suchpiston/cylinder arrangements.

Hence, the overall problem arises that, upon a directional reversal ofthe movement of the component, frictional forces have to be overcomethat are quite considerable, and that large additional masses have to beaccelerated and decelerated, respectively.

Especially in machine tools in which three-dimensional operatingmovements are to be created, this results in undesired flaws, e.g.so-called quadrant jumps in circles.

Further drawbacks arise with respect to the linear drives used in modernmachine tools. Such linear drives/linear motors are only able to applysmall holding forces so that a weight compensation as well as measuresfor the respective mounting are indispensable in the case of verticallymovable components.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a weightcompensating device of the above-mentioned type which with a simpleconstruction and at low manufacturing costs allows for a weightcompensation also in the case of a very dynamic movement of thecomponent while avoiding the drawbacks of the prior art.

Accordingly, this object is achieved by providing a weight compensatingdevice comprising: a carrier and a component having arrangedthereinbetween at least one negative pressure body of a variable lengthwhich is connected to a negative pressure source for compensating theweight acting on the component.

The weight compensating device of the invention is characterized by anumber of considerable advantages.

First of all, it should be noted that the solution of the inventioncreates virtually no friction so that even with very dynamic movementsof the component, which is e.g. provided with linear drives, a highpositioning accuracy can be accomplished. In machine tools this means avery high contour fidelity in the case of such very dynamic axial unitsor axes comprising the said component.

The negative pressure body of the invention is preferably configured inthe form of a vacuum hose. One or several vacuum hoses of such a typemay be mounted on the component such that they compensate part of theweight or the whole weight of the component.

Such vacuum hoses can be produced at very low costs. These areconventional standardized constructional elements. Vacuum hoses are e.g.known in connection with lifting and transportation in transportengineering. They can vary their length within wide ranges, and acollapsing of the vacuum hose due to the external air pressure isavoided by a spiral spring or the like, which is introduced into thewall of the vacuum hose to stabilize the vacuum hose. The vacuumprevailing in the vacuum hose thus acts in axial direction only.

Hence, the negative pressure body of the invention does not impair themovability or movement of the component, but just compensates thegravity or weight thereof. Hence, very rapid and highly dynamicmovements are also possible and these effect a very high contourfidelity in the treatment of workpieces.

Preferably, the negative pressure source is connected via an accumulatorto the negative pressure body. Since the negative pressure (the vacuum)in the negative pressure body cannot be reduced at will for technicalreasons, the accumulator with its considerably enlarged volume forms abuffer. Preferably, the accumulator is connected to the negativepressure body via a line of a small cross-section, e.g. a smallconnection hose, which provides for permanent pressure compensationbetween the accumulator and the negative pressure body. Large changes involume in the negative pressure body (vacuum hose) during movement ofthe component have thus only a slight effect on the overall pressure ofthe vacuum in the negative pressure body and the accumulator becausethere is a very large volume of the overall system on the whole. Hence,this volume is hardly changed by the compression or decompression of thenegative pressure body.

A further essential advantage of the invention follows from the goodthermal characteristics. Hence, the weight compensating device of theinvention does not lead to an undesired heating up of specific parts ofthe total system, which in turn could limit the precision of themovement. Since only very small air masses are moved between thenegative pressure body and the accumulator, the air is hardly heated upeven in the case of a long-lasting, rapid and reversing movement of thecomponent. The low friction of the negative pressure body (vacuum hose)is also instrumental in virtually preventing any heating up of thenegative pressure volume, also in the case of very high loads.

These and other details, features and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses a preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawing which forms a part of the originaldisclosure:

FIG. 1 is a simplified perspective view of a machine tool using theweight compensating device of the invention.

DETAILED DESCRIPTION

A selected embodiment of the present invention will now be explainedwith reference to the drawings. It will be apparent to those skilled inthe art from this disclosure that the following description of theembodiment of the present invention is provided for illustration onlyand not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

FIG. 1 is a schematic perspective illustration showing a machine toolwith a machine bed 4 on which a portal 5 is supported. The machine bed 4has movably arranged thereon a table 6 which can carry a workpiece (notshown).

The portal 5 supports a carrier 1 which is laterally displaceable. Thecarrier 1, in turn, supports thereon a vertically movable component 2which forms an axial unit with a spindle 7 and a tool 8. The respectivedrives are not shown in detail for the sake of a clear illustration. Itfollows from the resulting movement paths that the tool 8 is movable inat least three axes relative to a workpiece.

As mentioned, the axial unit (component 2) is movable in verticaldirection relative to the carrier 1. It comprises lateral lower struts9, each having fastened thereto a negative pressure body 3 (vacuumhose). The upper end of the negative pressure body 3 (vacuum hose) isfastened to the carrier 1. The introduction of a vacuum into thenegative pressure body 3 is accomplished through connections 10 whichmay e.g. be configured in the form of hoses and are fastened to thecarrier 1. The hoses have a small cross-section and lower ends thatterminate in an accumulator 11 or tank. A drive or a vacuum pump 12 iscoupled to the accumulator 11.

It follows from the illustration of FIG. 1 that the weight of the axialunit 2 can be compensated through a symmetrical arrangement of the twonegative pressure bodies (vacuum hoses) 3.

The present invention is not limited to the illustrated embodiment.Rather, many alterations and modifications are possible within the scopeof the present invention.

1. A weight compensating device comprising: a carrier and a componentincluding a machining spindle which is supported on the carrier and isdisplaceable in at least a vertical direction relative to the carrier bya drive, the carrier and the component having arranged thereinbetween atleast one negative pressure body of a variable length which is connectedto a negative pressure source for compensating the weight acting on thecomponent.
 2. The weight compensating device according to claim 1,wherein the at least one negative pressure body is configured in theform of a vacuum hose.
 3. The weight compensating device according toclaim 2, wherein a plurality of vacuum hoses are provided.
 4. The weightcompensating device according to claim 3, wherein the negative pressuresource is connected via an accumulator to the at least one negativepressure body.
 5. The weight compensating device according to claim 1,wherein the negative pressure source is connected via an accumulator tothe at least one negative pressure body.
 6. The weight compensatingdevice according to claim 5, wherein the accumulator is connected via aline of a small cross-section to the at least one negative pressurebody.
 7. The weight compensating device according to claim 6, whereinthe carrier and the component are configured as part of a machine tool,the component including a drive unit.
 8. The weight compensating deviceaccording to claim 5, wherein the negative pressure source comprises avacuum pump coupled to a surface of the accumulator.
 9. The weightcompensating device according to claim 1, wherein the carrier and thecomponent are configured as part of a machine tool, the componentincluding a drive unit.
 10. The weight compensating device according toclaim 9 wherein the component has a longitudinal axis and forms an axialunit that is movable at least in the vertical direction relative to thecarrier.
 11. The weight compensating device according to claim 10,wherein the axial unit comprises at least one linear drive.
 12. Theweight compensating device according to claim 10, wherein at least twoof the negative pressure bodies are positioned in a symmetricalarrangement about the component to compensate the weight of the axialunit.
 13. The weight compensating device according to claim 9, whereinthe component is supported by a portal, which is supported by a machinebed.
 14. The weight compensating device according to claim 13, furthercomprising a table for carrying a workpiece movably arranged on themachine bed.
 15. The weight compensating device according to claim 14,wherein the component has a longitudinal axis and forms an axial unithaving the spindle and a tool and the table is movable in asubstantially horizontal direction relative to the carrier forpositioning under the spindle and the tool.
 16. The weight compensatingdevice according to claim 14, wherein the component has a longitudinalaxis and forms an axial unit with the spindle and a tool that is movableat least in the vertical direction relative to the carrier to positionthe spindle and tool in a vertical location over the machine bed. 17.The weight compensating device according to claim 13, wherein the portalcomprises a symmetrical arrangement for supporting the carrier.
 18. Theweight compensating device according to claim 9, wherein the componenthas a longitudinal axis and forms an axial unit that comprises at leastone linear drive.
 19. The weight compensating device according to claim1, wherein at least one vacuum hose is fastened to the carrier by atleast one connection to introduce a vacuum into the at least onenegative pressure body.